Spark plug



April 1'4, DAVIS SPARK PLUG Filed y 7. 192

INVENTOR. 0A W ATTORNEYS,

Patented Apr. 14, 1925'.

UNITED STATES PATENT; orrlcu.

sn'nnnn s. Dawson scorn: PAsADENA,

camronmn.

sranx 1 mm.

Application filed May 7,

States,

that will give a double spark and will thereobjects and advantages ofthe invention will illustrated in th fore he better adapted to ignite acharge even under unfavorable conditions. Further appear as thespecification proceeds. v The preferred form of .my invention is eaccompanying drawing, in which Figure 1 shows a vertical sectionthroughthe spark tive view of an insulating element having v I oneelectrode and another element forming celain,

the principal part-otmy invention connected therewith; and Figure 3 aperspective detail view of the latter element. While I have shown onlythe preferred form'of the invention, I wish to have it understood thatvarious changes or modifications may-be made within the scope of theclaim hereto attached without departing from the spirit of theinvention.

In its main structural features my spark plug does notess'entiallydiffer from spark plugs now commonly used, and comprises a metallicshell 1) threaded at its lower end as shown at (2) adapted to be screwedinto a registeringperforation in the cylinder, not shown in the drawing,and a bushing (3) made of insulating material, preferably porw'ith agland (4) threadedly engaging the top of the shell as shown at (6) andhearing on a shoulder (7-) of the bushing with an asbestos packing (8)interposed between the gland and .the shoulder. metal shell has'a in (9)extending from its lower end, which 'atter is bent to extend into thevicinity of the rod (11) extending centrally through the porcelainbushing and pro'ectin from its lower end asshown at (12). T e upper endof this rod forms a plug; Figure 2 a perspec- The th 1923. Serial-R0.637,378.

terminal to which a wire maybe attached be tween the two nuts (13) and(14). The pin (9) and the lower end of the rod (1l) form two electrodesof a circuit includinga source of power, the body of the cylinder towhich the pin (9) is grounded and a wire connecting the source of powerwith the upper end of the rod (11). The two electrodes leave a gapbetween thesa e across which a spark is caused to jump when a highvoltage current is .passedthrough the circuit.

Iy invention conslsts in its principal-few -'tures in the introductionof a third metal element (16) disposed in such a manner as to extendinto the gap and to thus form a stepping-stone for the spark so thatinstead of asingle spark two sparks will be produced, one between theelectrode (12) and the third element, and the other between theelectrode (9) and the third element. The third element may assumemanydifferent forms, and the preferred form is shown in the drawing ascomprising a loop (17) adapted to engage an annular groove 18) in theinsulating bushing from one end of which extends a projection (19) bentas shown at (21) to extend into the gap.

The double spark thus produced will be hotter than a single spark wouldbe and therebyinsures proper ignition of a charge of lower grade. Anarrangement of this character also allows a good spark to he producedfrom a comparatively weak source of energy. The electrode (9) might alsobe omitted and the spark caused to jump from the loop (17) directly tothe shell '(1).

' I claim:

A spark plug comprising an insulating core, a metallic shell carryingthe core, a main electrode projecting from the lower end of the core, asecond electrode projecting inwardly from the lower end of the s ell toa point below and at one side of the main electrode, a metallic loopembracing e core, and a projection on the loop and extending across thelower end of the main electrode to provide a gap between the two andhaving its free end spaced from the second electrode to form a gaptherebtween.

SELDEN s. DAVIS.

